Comment 17 for bug 1869006

Alex, thanks for the quick answer, but sadly I still do not fully understand the implications, even if I read the pdf paper on RH website you mention, as well as the vendor advisory at https://support.hpe.com/hpesc/public/docDisplay?docId=emr_na-c04781229

When you say "qemu has no support", do you actually mean "qemu people are unable to help you if you break things by bypassing the in-place restrictions", or "qemu is designed to not work when restrictions are bypassed"?

Do I understand correctly that the BIOS can modify portions of the system usable RAM, so the vendor specific software tools can read those addresses, and if yes, does this mean is there a risk for data corruption if the RMRR restrictions are bypassed?

I have eventually managed to passthrough an nvidia card in the microserver gen8 to a windows vm using patched kernel 5.3, along with the vendor instructions to exclude the pcie slot aka the conrep solution but for it to work it still needed the "rmrr patch" aka removing the "return -EPERM" line below the "Device is ineligible [...]" in drivers/iommu/intel-iommu.c

However applying the same modification to kernel 5.4 leads to the "VFIO_MAP_DMA: -22" error.

Is there other place in the kernel 5.4 source that must be modified to bring back the v5.3 kernel behaviour? (ie. I have a stable home windows vm with the gpu passthrough despite all)